You might want to compare the SHA256 checksums or the MD5 checksums to verify the integrity of downloaded packages.
The SHA256 checksums should be favored as the MD5 algorithm must be treated as insecure!

Note: After upgrading VirtualBox it is recommended to upgrade the guest additions as well.

User Manual

The VirtualBox User Manual is included in the VirtualBox binaries above. If, however, you would like to take a look at it without having to install the whole thing, you also access it here:

VirtualBox older builds

The binaries in this section for VirtualBox before version 4.0 are all released under the VirtualBox Personal Use and Evaluation License (PUEL). As of VirtualBox 4.0, the Extension Pack is released under the VirtualBox Personal Use and Evaluation License and the other packages are released under the terms of the GPL version 2. By downloading, you agree to the terms and conditions of the respective license.

VirtualBox Sources

The VirtualBox sources are available free of charge under the terms and conditions of the GNU General Public License, Version 2. By downloading from the below links, you agree to these terms and conditions.